PIONEER COMMUNITIES 143 
Ecologically one of the most interesting insects is a caddis-worm 
(Leptoceridae), which creeps over the Chara and submerged wood. 
It (Fig. 93) has a case made of the minutest sand grains and pieces of 
humus, such as are stirred up by the waves and which are to be found 
REPRESENTATIVES OF A YOUNG POND COMMUNITY 
Fic. 86.—The shell of a mussel (Anodonta grandis footiana) that has been broken 
open by a muskrat; slightly enlarged. 
Fic. 87.—The burrowing dragon-fly nymph (Gomphus spicatus), with the mask 
extended. 
Fic. 88.—Some fishes of the pond. The dark fish which rests near the bottom is 
the mud minnow (Umbra limi). The fish swimming about is the golden shiner 
(Abramis crysoleucas); 1/5 natural size. 
among the chara. This species is the successor of the bottom species 
(Goera). It belongs to a different group and has structural characters 
which distinguish it from Goera, but which probably have no relation 
to its habitat or habits. On the other hand, the mores as indicated by 
case-building is also different but is related to the environment. The 
